Image processing apparatus, image processing method, providing medium and presentation system

ABSTRACT

An image including a bright point which is specified in another image on a screen is captured. An image processing apparatus applies threshold processing to the pixel values of the captured image to determine the position of the bright point. The image processing apparatus calculates the logical product of a pixel value in the current frame line and that in the line one frame line before (or after) for binarization in the unit period of the blinking pattern of the bright point having a margin of one frame to detect the blinking pattern of the bright point.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to image processing apparatuses,image processing methods, providing media, and presentation systems, andmore particularly, an image processing apparatus, an image processingmethod, a providing medium, and a presentation system which allow aspecified position on a display screen and the state of the specifiedposition to be simultaneously recognized.

[0003] 2. Description of the Related Art

[0004] Electronic presentations have been widely performed withprojectors and personal computers (PCs) having presentation software. Insuch an electronic presentation, a part of an image projected on ascreen may be specified by the use of a pointer or a laser pointer inmany cases.

[0005] A speaker operates a mouse or a remote commander using electronicwaves or infrared light for a PC to execute presentation softwareinstalled in the PC. Alternatively, the speaker asks another person tooperate the PC. In the presentation software, a predetermined positionon the screen is related to an operation of the PC in advance, andappropriate processing is performed.

[0006] Japanese Unexamined Patent Publication No. Hei-6-308879 disclosesthat when a speaker specifies a position on a display screen by apointer, the pointer receives light emitted by a photoelectricconversion device installed on the display screen or in the vicinity ofthe screen, the axial direction of the pointer is calculated from thelight, and a pointer mark is displayed in the axial direction on thescreen.

[0007] Japanese Unexamined Patent Publication No. Hei-8-95707 disclosesthat when a speaker specifies a position on a display screen by apointer, the shade of the pointer is captured by an infrared camera, andthe tip position of the pointer is detected to obtain the specifiedposition.

[0008] Japanese Unexamined Patent Publication No. Hei-9-120340 disclosesthat when a speaker specifies a position on a display screen by a laserbeam, the spot diameter of the laser beam on the display screen ischanged, and the specified position is detected from differences intiming when devices disposed at three corners of the screen detect thechange of the spot diameter.

[0009] Japanese Unexamined Patent Publication No. Hei-10-39994 disclosesthat when a speaker specifies a position on a display screen, theposition of the speaker, the inclination of the speaker, the positionwhere the speaker views are detected to obtain the specified position.

[0010] In these conventional technologies, however, only the positionspecified by a pointing device is detected, but image information at theposition cannot be obtained.

[0011] In addition, a complicated apparatus is required to detect theposition and the angle of a screen and the position specified by apointing device.

SUMMARY OF THE INVENTION

[0012] The present invention has been made in consideration of the abovesituations. Accordingly, it is an object of the present invention toprovide an image processing apparatus, an image processing method, aproviding medium, and a presentation system which allow a positionpointed by a pointing device on a displayed image and image informationat the position to be simultaneously detected.

[0013] Another object of the present invention is to provide a simpleimage processing apparatus which allows the position and the angle of ascreen and a position pointed by a pointing device on a displayed imageto be detected.

[0014] One of the foregoing object is achieved in one aspect of thepresent invention through the provision of an image processing apparatusincluding position determination means for determining from imageinformation indicating a captured second image which includes a brightpoint disposed on a first image the position of the bright point, andblinking-pattern detection means for binarizing the image information todetect the blinking pattern of the bright point disposed on the firstimage.

[0015] One of the foregoing object is achieved in another aspect of thepresent invention through the provision of an image processing methodincluding a position determination step of determining from imageinformation indicating a captured second image which includes a brightpoint disposed on a first image the position of the bright point, and ablinking-pattern detection step of binarizing the image information todetect the blinking pattern of the bright point disposed on the firstimage.

[0016] One of the foregoing object is achieved in yet another aspect ofthe present invention through the provision of a providing medium forproviding a computer-readable program which makes an image processingapparatus execute processing, the processing including a positiondetermination step of determining from image information indicating acaptured second image which includes a bright point disposed on a firstimage the position of the bright point, and a blinking-pattern detectionstep of binarizing the image information to detect the blinking patternof the bright point disposed on the first image.

[0017] According to the image processing apparatus, the image processingmethod, and the providing medium of the present invention, from imageinformation indicating a captured second image which includes a brightpoint disposed on a first image, the position of the bright point isdetermined, and the image information is binarized to detect theblinking pattern of the bright point. Therefore, both position andblinking pattern of the bright point can be detected.

[0018] One of the foregoing object is achieved in a further aspect ofthe present invention through the provision of an image processingapparatus for processing an image of an object having four points ofwhich the mutual relative positions are known, including firstcalculation means for calculating the gradient of the object in athree-dimensional space from the positions of the four points on theimage, and second calculation means for calculating the position of theobject in the three-dimensional space from the gradient of the object inthe three-dimensional space calculated by the first calculation meansand the distances between the four points.

[0019] One of the foregoing object is achieved in a yet further aspectof the present invention through the provision of an image processingmethod for an image processing apparatus that processes an image of anobject having four points of which the mutual relative positions areknown, including a first calculation step of calculating the gradient ofthe object in a three-dimensional space from the positions of the fourpoints on the image, and a second calculation step of calculating theposition of the object in the three-dimensional space from the gradientof the object in the three-dimensional space calculated in the firstcalculation step and the distances between the four points.

[0020] One of the foregoing object is achieved in a still further aspectof the present invention through the provision of a providing medium forproviding a computer-readable program which makes an image processingapparatus that processes an image of an object having four points ofwhich the mutual relative positions are known execute processing, theprocessing including a first calculation step of calculating thegradient of the object in a three-dimensional space from the positionsof the four points on the image, and a second calculation step ofcalculating the position of the object in the three-dimensional spacefrom the gradient of the object in the three-dimensional spacecalculated in the first calculation step and the distances between thefour points.

[0021] According to the image processing apparatus, the image processingmethod, and the providing medium of the present invention, the gradientof the object in the three-dimensional space is calculated from thepositions of the four points on the image, and the position of theobject in the three-dimensional space is calculated from the distancesbetween the four points and the gradient of the object in thethree-dimensional space. Therefore, the position and the angle of ascreen and a position pointed by a pointing device on a displayed imageare allowed to be detected by a simple apparatus.

[0022] One of the foregoing object is achieved in a yet still furtheraspect of the present invention through the provision of a presentationsystem including image display means for displaying a first image;pointing means for pointing a predetermined position on the first imageby a bright point; pickup means for capturing a second image whichincludes the bright point pointed on the first image; image processingmeans for determining the position of the bright point on the firstimage from image information indicating the second image and forbinarizing the image information to detect the blinking pattern of thebright point on the first image; and combination means for combining thefirst image correspondingly to the position of the bright point and theblinking pattern of the bright point detected by the image processingmeans.

[0023] According to the presentation system of the present invention,the predetermined position on the first image is specified by a brightpoint; the position of the bright point on the first image is determinedfrom image information indicating the second image which includes thebright point specified on the first image; the image information isbinarized to detect the blinking pattern of the bright point on thefirst image; and the first image is combined correspondingly to theposition and the blinking pattern of the detected bright point.Therefore, the image corresponding to the position and the blinkingpattern of the bright point can be instantaneously displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a block diagram of a presentation system according to anembodiment of the present invention.

[0025]FIG. 2 is a block diagram of an image processing apparatus shownin FIG. 1.

[0026]FIG. 3 is a flowchart of an image processing method for the imageprocessing apparatus shown in FIG. 2.

[0027]FIG. 4 is a view showing coordinate compensation processingperformed in a step S1 to a step S6 shown in FIG. 3.

[0028]FIG. 5 is a view showing processing for detecting the blinkingpattern of a bright point in a step S13 shown in FIG. 3.

[0029]FIG. 6 is a flowchart of another image processing method for theimage processing apparatus 4.

[0030]FIG. 7 is a view showing vanishing points.

[0031]FIG. 8 is a view showing processing for calculating the gradientof a screen 1.

[0032]FIG. 9 is a side view of a video camera 3 and the screen 1.

[0033]FIG. 10 is a view showing a flow pickup method.

[0034]FIG. 11 is another view showing the flow pickup method.

[0035]FIG. 12 is still another view showing the flow pickup method.

[0036]FIG. 13 is a view of an image having a synchronization error.

[0037]FIG. 14 is another view of the image having the synchronizationerror.

[0038]FIG. 15 is still another view of the image having thesynchronization error.

[0039]FIG. 16 is a view showing synchronization-error compensationprocessing.

[0040]FIG. 17 is a view showing processing for detecting the positionsof bright points.

[0041]FIG. 18 is a view of the arrangement of the bright points.

[0042]FIG. 19 is a view showing processing for detecting the state of abright point.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Embodiments of the present invention will be described below. Toclarify the relationship between each means specified in claims and thefollowing embodiments, features of the present invention will bedescribed first with an embodiment (only one example) corresponding toeach means being added after the means in parentheses. The followingdescription does not mean that each means is limited to the writtenexample.

[0044] An image processing apparatus of the present invention includesposition determination means (for example, a step S1 to a step S12 shownin FIG. 3) for determining from image information indicating a capturedsecond image which includes a bright point disposed on a first image theposition of the bright point, and blinking-pattern detection means (forexample, a step S13) for binarizing the image information to detect theblinking pattern of the bright point disposed on the first image.

[0045] An image processing apparatus of the present invention includesfirst calculation means (for example, a step S37 shown in FIG. 6) forcalculating the gradient of an object in a three-dimensional space fromthe positions of four points on an image, and second calculation means(for example, a step S38 shown in FIG. 6) for calculating the positionof the object in the three-dimensional space from the gradient of theobject in the three-dimensional space calculated by the firstcalculation means and the distances between the four points.

[0046] A presentation system of the present invention includes imagedisplay means (for example, a screen 1 shown in FIG. 1) for displaying afirst image; pointing means (for example, a pointer 2 shown in FIG. 1)for pointing a predetermined position on the first image by a brightpoint; pickup means (for example, a video camera 3 shown in FIG. 1) forcapturing a second image which includes the bright point pointed on thefirst image; image processing means (for example, an image processingapparatus 4 shown in FIG. 1) for determining the position of the brightpoint on the first image from image information indicating the secondimage and for binarizing the image information to detect the blinkingpattern of the bright point on the first image; and combination means(for example, a personal computer 5 shown in FIG. 1) for combining thefirst image correspondingly to the position of the bright point and theblinking pattern of the bright point detected by the image processingmeans.

[0047] First Embodiment

[0048] A presentation system according to an embodiment of the presentinvention will be described below by referring to the drawings. FIG. 1is a block diagram showing a structure of the presentation system.

[0049] In the presentation system of the present embodiment, a speakermakes a presentation while the speaker specifies a position on an imagedisplayed on a screen 1 by a pointer 2, and a video camera 3 capturesthe condition. An image processing apparatus 4 detects the position of abright point in an image captured by the video camera 3 and the blinkingpattern of the bright point made while time elapses, and sends the bitpattern corresponding to the blinking pattern to a personal computer 5.The personal computer 5 receives the position of the bright point andthe bit pattern indicating the blinking pattern of the bright point madewhile time elapses, processed by the image processing apparatus 4, andgenerates a combined image corresponding to the position of the brightpoint and the bit pattern indicating the blinking pattern of the brightpoint. A projector 6 projects image information sent from the personalcomputer 5 onto the screen 1.

[0050]FIG. 2 is a block diagram of the image processing apparatus 4. ACPU 21 executes various types of processing according to programs storedin a ROM 22. A RAM 23 stores data and programs required for the CPU 21to execute the various types of processing. An input and outputinterface 24 reads image information sent from the video camera 3 andoutputs image information to the personal computer 5.

[0051] The operation of the presentation system according to the presentembodiment will be described next.

[0052] The personal computer 5 sends image information indicating animage prepared by the speaker for the presentation to the projector 6.The projector 6 projects the image indicated by the image informationonto the screen 1. The projected image has a different luminance, adifferent color, and a different pattern from an image surrounding thescreen 1.

[0053] The speaker makes the presentation while the speaker specifiespositions on the projected image with the use of the pointer 2. Thispointer 2 is provided with a light-emitting device (LED) at its tip. Thespeaker operates the pointer such that the light-emitting device emitslight to show bright points on the image to clearly indicate thespecified positions to the audience.

[0054] When the speaker specifies a predetermined part of the image bythe pointer 2 and shows a bright point on the image, the video camera 3captures the entire screen 1, which displays the image including thebright point. Image information indicating the captured image is sent tothe image processing apparatus 4.

[0055] Processing of the sent image information, to be performed in theimage processing apparatus 4 shown in FIG. 2 will be described next byreferring to a flowchart shown in FIG. 3.

[0056] In a step S1, the CPU 21 extracts an image in an area showing thescreen 1 from the captured image. Since the luminance, the color, andthe pattern of the image projected onto the screen 1 differ from thoseof the image surrounding the screen 1, the image in the area showing thescreen 1 and the image in the area surrounding the screen 1 can beeasily determined. Therefore, the image in the area showing the screen 1can be easily extracted.

[0057] Then, the coordinates of the four corners of the area showing thescreen 1 are determined in a step S2 to a step S5.

[0058] In the step S2, the CPU 21 extracts the edges of the area showingthe screen 1. Then, in a step S3, the CPU 21 applies thresholdprocessing to the pixel values of the image information of the edges tobinarize the image information. In a step S4, the CPU 21 applies Houghtransform to the binarized image information of the edges to detect thefour sides of the area showing the screen 1.

[0059] In the step S5, the CPU 21 obtains the intersections of thedetected four sides, regards the intersections, “a,” “b,” “c,” and “d,”as the four corners of the area showing the screen 1, as shown in FIG.4, and calculates the coordinates (hereinafter also called coordinatesin an image coordinate system) of the points “a,” “b,” “c,” and “d” onthe captured image.

[0060] Next, a coordinate compensation parameter δ used for convertingthe coordinates of any point on the captured image to those on thescreen 1 is calculated in a step S6. The CPU 21 also executes thisprocessing.

[0061] As shown in FIG. 4, the coordinates of the intersection “e” of adiagonal line “bd” and a diagonal line “ac” of a figure “abcd” formed ofthe detected four-corner points “a,” “b,” “c,” and “d” are calculated.

[0062] Vanishing points U(x_(u), y_(u)) and V(x_(v), y_(v)) are obtainedfrom the coordinates of the points “a,” “b,” “c,” and “d.”$\begin{matrix}{U = {\frac{{2{{de}}b_{p}} - {{{db}}e_{p}}}{{2{{de}}} - {{db}}} \equiv \left( {x_{u},y_{u}} \right)}} & (1) \\{V = {\frac{{2{{ce}}a_{p}} - {{{ca}}e_{p}}}{{2{{ce}}} - {{ca}}} \equiv \left( {x_{v},y_{v}} \right)}} & (2)\end{matrix}$

[0063] In the above expressions, ∥de∥ indicates the distance between thepoints “d” and “e,” ∥db∥ indicates the distance between the points “d”and “b,” b_(p) indicates the coordinates of the point “b,” e_(p)indicates the coordinates of the point “e,” ∥ce∥ indicates the distancebetween the points “c” and “e,” ∥ca∥ indicates the distance between thepoints “c” and “a,” a_(p) indicates the coordinates of the point “a,”c_(p) indicates the coordinates of the point “c,” and x_(u), y_(u),x_(v), and y_(v) indicate the x and y coordinates of the vanishingpoints U and V, respectively.

[0064] From the following expressions, p_(s) and q_(s) are obtained bythe use of the x and y coordinates of the vanishing points U and V,x_(u), y_(u), x_(v), and y_(v). $\begin{matrix}{p_{s} = \frac{{- y_{u}} + y_{v}}{{x_{u}y_{v}} - {x_{v}y_{u}}}} & (3) \\{q_{s} = \frac{x_{u} - x_{v}}{{x_{u}y_{v}} - {x_{v}y_{u}}}} & (4)\end{matrix}$

[0065] With the use of p_(s), q_(s), and the focal length “f” of thevideo camera 3, the coordinate compensation parameter δ, used forconverting coordinates in the image coordinate system to those in thescreen coordinate system, and the z coordinates, ZA and ZB, of thepoints “A” and “B” in the screen coordinate system corresponding to thepoints “a” and “b” in the image coordinate system are expressed in thefollowing ways. $\begin{matrix}{\delta = {{p_{s}\frac{Z_{A}}{f}x_{a}} + {q_{s}\frac{Z_{A}}{f}y_{a}} - Z_{A}}} & (5) \\{\delta = {{p_{s}\frac{Z_{B}}{f}x_{b}} + {q_{s}\frac{Z_{B}}{f}y_{b}} - Z_{B}}} & (6) \\{Z_{A} = \frac{\delta \cdot f}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}} & (7) \\{Z_{B} = \frac{\delta \cdot f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f}} & (8)\end{matrix}$

[0066] The coordinates of the points A and B are expressed in thefollowing ways. $\begin{matrix}{A = {\left( {x_{A},y_{A}} \right) \equiv \left( {{\frac{Z_{A}}{f}x_{a}},{\frac{Z_{A}}{f}y_{a}},Z_{A}} \right)}} & (9) \\{B = {\left( {x_{B},y_{B}} \right) \equiv \left( {{\frac{Z_{B}}{f}x_{b}},{\frac{Z_{B}}{f}y_{b}},Z_{B}} \right)}} & (10)\end{matrix}$

[0067] With the use of the expression (5) to the expression (10), thedistance, ∥AB∥, between the points A and B is obtained in the followingway. $\begin{matrix}\begin{matrix}{{{AB}}^{2} = \quad {\left\{ {\frac{\delta \quad x_{a}}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - {\frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f} \cdot \frac{x_{b}}{x_{a}}}} \right)} \right\}^{2} +}} \\{\quad {\left\{ {\frac{\delta \quad y_{a}}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - {\frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f} \cdot \frac{y_{b}}{y_{a}}}} \right)} \right\}^{2} +}} \\{\quad \left\{ {\frac{\delta \quad f}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - \frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f}} \right)} \right\}^{2}}\end{matrix} & (11)\end{matrix}$

[0068] When the left side of the expression (11) is set to (actualdistance between the points A and B)², an expression (12) is obtained.$\begin{matrix}{{\left\{ {\frac{\delta \quad x_{a}}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - {\frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f} \cdot \frac{x_{b}}{x_{a}}}} \right)} \right\}^{2} + \left\{ {\frac{\delta \quad y_{a}}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - {\frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f} \cdot \frac{y_{b}}{y_{a}}}} \right)} \right\}^{2} + \left\{ {\frac{\delta \quad f}{{x_{a}p_{s}} + {y_{a}q_{s}} - f}\left( {1 - \frac{{x_{a}p_{s}} + {y_{a}q_{s}} - f}{{x_{b}p_{s}} + {y_{b}q_{s}} - f}} \right)} \right\}^{2}} = \left( {{actual}{\quad \quad}{distance}\quad {between}\quad {the}\quad {points}\quad A\quad {and}\quad B} \right)^{2}} & (12)\end{matrix}$

[0069] The value of the focal length “f” of the video camera 3, which isknown, is substituted for “f” in the expression (12) to obtain thecoordinate compensation parameter δ.

[0070] Then, the position of the bright point in the image coordinatesystem is converted to that of the bright point in the screen coordinatesystem in a step S7 to a step S12.

[0071] In the step S7, the CPU 21 applies threshold processing to thepixel values of the captured image by the use of a first threshold tobinarize it. Then, in a step S8, the CPU 21 applies threshold processingto the variance condition of the pixels having pixel values equal to ormore than the first threshold, by the use of a second threshold. In astep S9, the CPU 21 determines whether a bright point exists in theimage. The CPU 21 determines that when the variance of the pixels havingpixel values equal to or more than the first threshold is equal to orless than the second threshold, a bright point exists; and the CPU 21determines when the variance is more than the second threshold, a brightpoint does not exist. When it is determined that a bright point exists,the procedure proceeds to a step S10. When it is determined that abright point does not exist, the procedure proceeds to a step S13.

[0072] In the step S10, the CPU 21 measures the coordinates of an area(bright point “p”) where it has been determined that the bright pointexists in the image. Since the bright point has the area, a plurality ofcoordinates are obtained.

[0073] In a step S11, the CPU 21 calculates the averages of all thecoordinates of the bright point “p,” which have been obtained in thearea of the bright point, and regards the averages as the coordinates(x_(p), y_(p)) of the bright point “p” in the image.

[0074] In the step S12, the CPU 21 obtains the coordinates (X_(p),Y_(p), Z_(p)) of the point “P” on the screen 1 in the three-dimensionalspace, which are expected from the coordinates (x_(p), y_(p)) of thebright point “p” in the image. The Z coordinate Z_(p) of the point P canbe expressed in the following way by the use of the coordinatecompensation parameter δ. $\begin{matrix}{{Zp} = \frac{\delta \cdot f}{{x_{p}p_{s}} + {x_{p}q_{s}} - f}} & (13)\end{matrix}$

[0075] The three-dimensional coordinates of the expected point “P” onthe screen 1 can be obtained from the following expression (14) or (15).$\begin{matrix}{P = \left( {{\frac{Z_{P}}{f}x_{p}},{\frac{Z_{P}}{f}y_{p}},Z_{p}} \right)} & (14) \\{P^{\prime} = \left( {{\frac{\overset{\_}{AB}}{{AB}} \cdot \overset{\_}{AP}},{\frac{\overset{\_}{AD}}{{AD}} \cdot \overset{\_}{AP}}} \right)} & (15)\end{matrix}$

[0076] In a step S13, the blinking pattern of the bright point obtainedwhen time elapses is detected.

[0077] The unit period (ON period or OFF period) of the blinking patternof a bright point which the light-emitting device disposed at the tip ofthe pointer 2 generates has a margin. This is because, since it isgenerally considered that the period of the blinking time pattern of thebright point is not synchronized with the period when an image capturesection captures pixels in the input and output interface 24 of theimage processing apparatus 4, the blinking pattern of the bright pointis prevented from being erroneously detected due to this synchronizationerror. In the present embodiment, the unit period of the blinkingpattern of the bright point has a margin of one vertical drive period(VD, field period, which equals {fraction (1/60)} seconds in the NTSCsystem) and the unit period is set to 2 VDs or longer. FIG. 5(A) showsthe blinking pattern of a bright point (LED). In this example, the ONperiod and the OFF period are set to multiples of (n times where n is aninteger) 2 VDs. FIG. 5(B) shows a result obtained when the blinkingpattern of the bright point (LED) shown in FIG. 5(A) is captured.

[0078] In the step S13, the CPU 21 calculates the logical product of apixel value in the current field line and that in the line one fieldbefore (or one field after), and determines that a bright point existsonly when both values are ON. This eliminates an erroneous detectioncaused by the synchronization error of the periods. FIG. 5(C) shows thebit pattern of the binarization result obtained from the capturedblinking pattern of the bright point shown in FIG. 5(B) by the imageprocessing apparatus 4 with the synchronization error being eliminated.One bit is obtained in every 2 VDs (one frame).

[0079] In a step S14, the CPU 21 sends the obtained bit patternindicating the blinking pattern of the bright point to the personalcomputer 5.

[0080] In a step S15, the CPU 21 determines whether the speaker hasfinished the presentation, namely, whether it is necessary to applyprocessing to the image including the bright point which the speaker hasspecified. When it is determined that it is not necessary, theprocessing is terminated. When it is determined that it is necessary,the procedure returns to the step S7, and the above operations, that is,the processing from the step S7 to the step S15, are repeatedlyexecuted.

[0081] As described above, the image processing apparatus 4 sends thebit pattern indicating the blinking pattern of the bright point as wellas the position of the bright point generated by the pointer 2 to thepersonal computer 5.

[0082] Another processing to be performed by the image processingapparatus 4, which sends the bit pattern indicating the blinking patternof the bright point and the position of the bright point generated bythe pointer 2 to the personal computer 5, will be described next byreferring to a flowchart shown in FIG. 6. Since processing in a step S31to a step S35 is the same as the processing from the step 1 to the stepS5 shown in FIG. 3, descriptions thereof will be omitted.

[0083] In a step S36, the CPU 21 calculates vanishing points from theimage on the screen 1. Processing in the CPU 21 for calculatingvanishing points from the image on the screen 1 will be described byreferring to FIG. 7. In the following description, an image coordinatesystem has the origin at the point of view of the video camera 3.

[0084] As shown in FIG. 7, a vanishing point U(x_(u), y_(u)) is anintersection of a line “ab” passing a point “a” and a point “b” on theimage plane and a line “cd” passing a point “c” and a point “d,” and avanishing point V(x_(v), y_(v)) is an intersection of a line “ad”passing a point “a” and a point “d” and a line “bc” passing a point “b”and a point “c.”The line “ab” is expressed by an expression (16), theline “cd” is expressed by an expression (17), the line “ad” is expressedby an expression (18), and the line “bc” is expressed by an expression(19).

α₁ x+β ₁ y=γ ₁  (16)

α₂ x+β ₂ y=γ ₂  (17)

α₃ x+β ₃ y=γ ₃  (18)

α₄ x+β ₄ y=γ ₄  (19)

[0085] Therefore, the coordinates of the vanishing point U(x_(u), y_(u))are calculated by an expression (20) and an expression (21), and thecoordinates of the vanishing point V(x_(v), y_(v)) are calculated by anexpression (22) and an expression (23).

x _(u)=(β₂γ₁−β₁γ₂)/(α₁β₂−α₂β₁)  (20)

y _(u)=(α₁γ₂−α₂γ₁)/(α₁β₂−α₂β₁)  (21)

x _(v)=(β₄γ₃−β₃γ₄)/(α₃β₄−α₄β₃)  (22)

y _(v)=(α₃γ₄−α₄γ₃)/(α₃β₄−α₄β₃)  (23)

[0086] When the coordinates of the point “a” are set to (x₁, y₁), thecoordinates of the point “b” are set to (x₂, y₂), the coordinates of thepoint “c” are set to (x₃, y₃), and the coordinates of the point “d” areset to (x₄ y₄) on the image, α₁, β₁, γ₁, α₂β₂, γ₂, α₃, β₃, γ₃, α₄, β₄,and γ₄ are calculated by an expression (24), an expression (25), anexpression (26), an expression (27), an expression (28), an expression(29), an expression (30), an expression (31), an expression (32), anexpression (33), an expression (34), and an expression (35),respectively.

α₁ =y ₁ −y ₂  (24)

β₁=−(x ₁ −x ₂)  (25)

γ₁ =x ₂ y ₁ −x ₁ y ₂  (26)

α₂ =y ₃ −y ₄  (27)

β₂=−(x ₃ −x ₄)  (28)

γ₂ =x ₄ y ₃ −x ₃ y ₄  (29)

α₃ =y ₁ −y ₄  (30)

β₃=−(x ₁ −x ₄)  (31)

γ₃ =x ₄ y ₁ −x ₁ y ₄  (32)

α₄ =y ₂ −y ₃  (33)

β₄=−(x ₂ −x ₃)  (34)

γ₄ =x ₃ y ₂ −x ₂ y ₃  (35)

[0087] In a step S37, the CPU 21 calculates the gradient of the screen 1from the vanishing point U(x_(u), y_(u)) and the vanishing pointV(x_(v), y_(v)). As shown in FIG. 8, an image coordinate system isspecified such that the z axis of the image coordinate system isperpendicular to the image plane and the image plane is disposed at z=1in the image coordinate system so that coordinate points in the imagecoordinate system can be normalized by the focal length “f” of the lens.A point P_(a)(x_(a), y_(a), z_(a)) in a space is projected to a pointp_(a)(x_(a)/z_(a), y_(a)/z_(a)) on the image plane by perspectivetransformation.

[0088] A point P₁ on a line L which passes the point P_(a) and has adirection vector v=(v_(x), v_(y), v_(z)) is expressed by an expression(36), and a point p₁ generated by projecting the point P₁ onto the imageplane is expressed by an expression (37). $\begin{matrix}\begin{matrix}{P_{1} = \quad {P_{a} + {tv}}} \\{= \quad \left( {{x_{a} + {tv}_{x}},{y_{a} + {tv}_{y}},{z_{a} + {tv}_{z}}} \right)}\end{matrix} & (36) \\\begin{matrix}{p_{1} = \quad \left( {{\left( {x_{a} + {tv}_{x}} \right)/\left( {z_{a} + {tv}_{z}} \right)},{\left( {y_{a} + {tv}_{y}} \right)/\left( {z_{a} + {tv}_{z}} \right)}} \right)} \\{= \quad \left( {{\left( {{x_{a}/t} + v_{x}} \right)/\left( {{z_{a}/t} + v_{z}} \right)},{\left( {{y_{a}/t} + v_{y}} \right)/\left( {{z_{a}/t} + v_{z}} \right)}} \right)}\end{matrix} & (37)\end{matrix}$

[0089] Since a vanishing point is a projection image obtained when aline having a direction vector is extended toward the infinity, p₁obtained when t becomes the infinity is a vanishing point and expressedby an expression (38). $\begin{matrix}\begin{matrix}{{\lim\limits_{t\rightarrow\infty}p_{1}} = \quad {\lim\limits_{t\rightarrow\infty}\left( {{\left( {{x_{a}/t} + v_{x}} \right)/\left( {{z_{a}/t} + v_{z}} \right)},{\left( {{y_{a}/t} + v_{y}} \right)/\left( {{z_{a}/t} + v_{z}} \right)}} \right)}} \\{= \quad \left( {{v_{x}/v_{z}},{v_{y}/v_{z}}} \right)}\end{matrix} & (38)\end{matrix}$

[0090] Since the normal vector n(p_(s), q_(s), −1) of a plane π in thespace is perpendicular to the direction vector u(u_(x), u_(y), u_(z)) ofany line on the plane π, the following expression (39) is satisfied, andan expression (40) is obtained from the expression (39) (hereinafter, avariable with an arrow disposed thereabove indicates a vector).

{right arrow over (n)}·{right arrow over (u)}=p _(s) u _(x) +q _(s) ·u_(y) −u _(z)=0  (39)

p _(s)(u _(x) /u _(z))+q _(s)(u _(z) /u _(z))=1  (40)

[0091] In the expression (40), (u_(x)/u_(z)) and (u_(y)/u_(z)) indicatea vanishing point as shown in the expression (38). Since the directionvector u can be any vector, the expression (40) indicates a set ofvanishing points on the image plane, namely, a vanishing line.Conversely, when a vanishing line is expressed by an expression ofax+by=1, the gradient of a plane having this vanishing line is (a, b,−1). Therefore, the vanishing line is obtained by an expression (41)with the use of the vanishing points U(x_(u), y_(u)) and V(x_(v), y_(v))calculated from the quadrangle “abcd,” which is a projection image ofthe quadrangle “ABCD.”

((−y _(u) +y _(v))/(x _(u) y _(v) −x _(v) y _(u)))x+((x _(u) −x _(v))/(x_(u) y _(v) −x _(v) y _(u)))y=1  (41)

[0092] The normal vector n_(abcd) of the quadrangle “ABCD” can beexpressed by an expression (42).

{right arrow over (n)} _(abcd)=((−y _(u) +y _(v))/(x _(u) y _(v) −x _(v)y _(u)),(x _(u) −x _(v))/(x _(u) y _(v) −x _(v) y _(u)),−1)  (42)

[0093] The normal vector n_(abcd) is normalized to obtain a vector$\begin{matrix}{\overset{\rightarrow}{N} = \frac{{\overset{\rightarrow}{n}}_{abcd}}{{\overset{\rightarrow}{n}}_{abcd}}} & (43)\end{matrix}$

[0094] In this expression, an operator ∥vector∥ indicates an operatorfor obtaining the absolute value of the vector.

[0095] As described above, the CPU 21 calculates the gradient of thescreen 1 from the image on the screen 1.

[0096] In a step S38, the CPU 21 obtains the distance from the videocamera 3 to the screen 1 according to the gradient of the screen 1. FIG.9 is a side view of the video camera 3 and the screen 1. The distanced_(a) between an origin “o” of the image coordinate system, which iscalculated from the point “a,” and the origin “O” of the screencoordinate system is calculated from an expression (44).

d _(a)=(∥AE∥ sin θ_(a))/(sin(θ_(a)+φ_(a)))  (44)

[0097] In this expression, ∥AE∥ is known, θ_(a) is defined by anexpression (45), and φ_(a) is defined by an expression (46).

θ_(a)=⊃oEA  (45)

φ_(a)=⊃oAE  (46)

[0098] In the same way, the distance d_(b) between an origin “o” of theimage coordinate system, which is calculated from the point “b,” and theorigin “O” of the screen coordinate system, the distance d_(c) betweenan origin “o” of the image coordinate system, which is calculated fromthe point “c,” and the origin “o” of the screen coordinate system, andthe distance d_(d) between an origin “o” of the image coordinate system,which is calculated from the point “d,” and the origin “O” of the screencoordinate system, are calculated. The average of the distance d_(a),the distance d_(b), the distance d_(c), and the distance d_(d) is usedas the distance d_(ave) between the origin “o” of the image coordinatesystem and the origin “O” of the screen coordinate system.

[0099] A parallel movement vector “t” from the origin “o” of the imagecoordinate system to the origin “O” (the center of the quadrangle“ABCD”) of the screen coordinate system is calculated by an expression(47). $\begin{matrix}{\overset{\rightarrow}{t} = {d_{ave}\frac{\overset{\rightarrow}{oe}}{\overset{\rightarrow}{oe}}}} & (47)\end{matrix}$

[0100] As described above, the position (X_(m), Y_(m), Z_(m)) and theangle (Rx_(m), Ry_(m), Rz_(m)) of the screen 1 in the three-dimensionalspace are calculated from the position of the screen in the image. Inthe description of the processing for calculating the position and theangle of the screen 1, the image plane is disposed at z=1 in the imagecoordinate system. As shown in the expressions used in the descriptionfor FIG. 3, when p_(s) and q_(s) are compensated by the focal length “f”of the video camera 3, even if the video camera does not have a focallength “f” of 1, the correct position and the correct angle arecalculated.

[0101] Since processing from a step S39 to a step S48 is the same as theprocessing from the step S6 to the step S15 shown in FIG. 3,descriptions thereof will be omitted.

[0102] As described above, also in the processing described by referringto the flowchart shown in FIG. 6, the image processing apparatus 4 sendsthe bit pattern indicating the blinking pattern of a bright point aswell as the position of the bright point generated by the pointer 2 tothe personal computer 5.

[0103] The personal computer 5 assigns the detected bit pattern to acommand for controlling the personal computer 5. It is not necessarythat all of periods required to detect commands are the same. It isnecessary to promptly detect frequently used commands, but in manycases, it may take some time period to detect commands which are notfrequently used. Therefore, short bit patterns are assigned to thefrequently used commands, and relatively long bit patterns are assignedto the commands which are not frequently used in order to shorten thetotal detection time.

[0104] In the present embodiment, a pattern of “010” is assigned to astate in which a left button (not shown) of the pointer 2 is pressed, apattern of “0001” is assigned to a state in which a right button (notshown) of the pointer 2 is pressed, and to avoid an erroneous detection,a pattern of “01” is assigned to a state in which no button is pressed.When the number of buttons is increased, the number of patterns can beincreased in the same way.

[0105] The personal computer 5 sends the image information correspondingto the position and the blinking pattern of a bright point which thespeaker specifies, to the projector 6. The projector 6 projects thereceived image information onto the screen 1. For example, the positionwhere the speaker specifies is marked on the screen 1, and isimmediately moved on the screen when the bright point is moved as timeelapses, so that the position where the speaker specifies can bespontaneously indicated. The assignment can be made, for example, suchthat the projector 6 displays the next scene when the speaker moves thebright point to a predetermined position (for example, where an arrow isshown on the screen) and presses the left button of the pointer 2. Theassignment can be made, for example, such that the projector 6 displaysthe last scene when the speaker moves the bright point to the sameposition and presses the right button of the pointer 2.

[0106] Until the speaker finishes the presentation, the above operationsare repeated. When the speaker finishes the presentation, the aboveprocessing in the presentation system is finished.

[0107] As described above, in the presentation system of the presentembodiment, the captured image is binarized by applying the thresholdprocessing to the pixel values, and it is determined that a bright pointexists when the variance of pixels having pixel values equal to orgreater than the first threshold is equal to or smaller than the secondthreshold.

[0108] Therefore, points other than the bright point specified by thepointer 2 are prevented from being erroneously detected on the screen 1.

[0109] Since coordinates of an image projected onto the screen 1 iscompensated by the coordinate compensation parameter δ, used forconverting coordinates on a captured image to those on the screen 1,three-dimensional coordinates on the screen 1 can be correctly detected.

[0110] Since the blinking pattern of the bright point has a margin ofone field and the time pattern of the bright point is detected by thelogical product of the value of a pixel on the current field line andthat of the pixel on the line one field before, an erroneous detectioncaused by a synchronization error between the period of the blinkingpattern of the bright point and the period of the image capture sectionis avoided.

[0111] Therefore, the position and the blinking pattern of the brightpoint can be correctly detected from the captured image.

[0112] Since frequently used commands are made short when the personalcomputer 5 controls the position and the blinking pattern of thedetected bright point, a processing time required for reading apredetermined command (pattern) among many commands (patterns) isreduced.

[0113] Therefore, when the speaker specifies a position on an imageprojected onto the screen 1, by the use of the pointer 2, a processingtime required for displaying a picture indicating the position and theblinking pattern of a bright point specified on the image is reduced.

[0114] Positions can be immediately marked correspondingly to the traceof a bright point specified in an image on the screen 1.

[0115] Therefore, according to the presentation system of the presentembodiment, when the speaker makes a presentation by using an image, theaudience can immediately recognize a position which the speakerspecifies on the screen 1. The system provides easy-to-understandpresentations.

[0116] Second Embodiment

[0117] Whereas an image displayed on the screen 1 is captured as is inthe presentation system according to the first embodiment, the videocamera 3 captures an image on the screen 1 by a flow pickup method andthe image processing apparatus 4 detects the position and the blinkingtime pattern of a bright point in a presentation system according to asecond embodiment.

[0118] The presentation system according to the present embodimentdiffers from that of the first embodiment in a method for capturing theblinking pattern of a bright point in the video camera 3 and an imageprocessing method for detecting the position and the blinking pattern ofthe bright point in the image processing apparatus 4. The presentationsystem according to the present embodiment has the same structure asthat of the first embodiment.

[0119] The method for capturing the blinking pattern of a bright pointand the image processing method for detecting the position and theblinking pattern of the bright point in the present embodiment will bedescribed below.

[0120] A flow pickup method used in the video camera 3 will be describedfirst. The flow pickup method means a capture method in which the outputof a photodiode constituting each pixel is transferred to a verticaltransfer CCD a plurality of times during one field period in a CCDpickup device built in the video camera 3. Conversely, in a normalpickup method, the output of a photodiode constituting each pixel istransferred to the vertical transfer CCD only once during one fieldperiod.

[0121] Therefore, as shown in FIG. 10(A), for example, when a brightpoint is turned on for 12 horizontal scanning periods (HDs) and isturned off for the next 12 HDs, and this pattern is repeated twice inone field period, only one light-emitting point is captured if thenormal pickup method is used. When the video camera 3 captures thebright point by the flow pickup method and the output of a photodiodeconstituting each pixel is transferred to the vertical transfer CCDevery two HDs, however, the image obtained as a result shows a pluralityof light-emitting points in one field as shown in FIG. 10(C). In thisexample, a light-emitting point is set to have a three-line size on acaptured image.

[0122] When the image shown in FIG. 10(C) is output from the videocamera 3 to the image capture section of the image processing apparatus4, the image capture section applies capture processing to the image togenerate an image shown in FIG. 11. As described above, since alight-emitting point has a three-line size, the image of each outputoverlaps with those output immediately before and after, and theluminance of the pixel in the captured image is gradually changed.

[0123] When the image shown in FIG. 11 is output from the image capturesection to the image processing apparatus 4, the image processingapparatus 4 applies binarization processing to the image to generate animage shown in FIG. 12. In this case, luminance “A” and luminance “B” inthe image shown in FIG. 11 are changed to luminance “L,” and luminance“C” and luminance “D” are changed to luminance “H.” The pixel value of apixel having luminance “H” is encoded to “1” and the pixel value of apixel having luminance “L” is encoded to “0.”

[0124] As described above, luminance changes generated in a time mannertwice in one field period are converted to two spatial changes by theflow pickup method. In the present embodiment of the present invention,the state of a bright point is observed according to this principle.

[0125] A procedure for executing synchronization-error compensationprocessing in the image processing apparatus 4 will be described next.

[0126] The images shown in FIG. 10(C), FIG. 11, and FIG. 12 are capturedwhen the timing of the blinking pattern of the bright point issynchronized with the capture timing of the video camera 3 in the flowpickup method. On the other hand, if a synchronization error of 0.5lines occurs, an image shown in FIG. 13 is captured, for example,instead of the image shown in FIG. 10(C).

[0127] The image capture section of the image processing apparatus 4applies the capture processing to the image shown in FIG. 13 to covertit to an image shown in FIG. 14. The image processing apparatus 4 thenapplies the binarization processing to the image shown in FIG. 14 toconvert it to an image shown in FIG. 15. Whereas the blinking pattern ofthe bright point has six-line luminance “L” and six-line luminance “H”as shown in FIG. 12, the bright point is captured as shown in FIG. 15such that it has five-line luminance “L” and seven-line luminance “H.”In this case, luminance “A” and luminance “B” in the image shown in FIG.14 are changed to luminance “L,” and luminance “C,” luminance “D,” andluminance “E” are changed to luminance “H.” The pixel value of a pixelhaving luminance “H” is encoded to “1” and the pixel value of a pixelhaving luminance “L” is encoded to “0.”

[0128] The image processing apparatus 4 applies synchronization-errorcompensation processing to the image shown in FIG. 15 to covert it to animage which correctly shows the blinking pattern of the bright point asshown in FIG. 10(C). The image processing apparatus 4 reads a pixelvalue “0” in a line L5 in the image shown in FIG. 15 and reads a pixelvalue “0” in a line L4, which is one line before the line L5, as shownin FIG. 16 which displays an expanded part of FIG. 15.

[0129] The image processing apparatus 4 obtains the logical product ofthe two read pixel values “0” and sets a pixel value in a new image(image obtained after the synchronization error is compensated for) tothe result “0.”

[0130] The image processing apparatus 4 reads a pixel value “1” in aline L6 in the image shown in FIG. 15 and reads a pixel value “0” in theline L5, which is one line before the line L6. The image processingapparatus 4 obtains the logical product of the two read pixel values “1”and “0,” and sets the pixel value corresponding to the line L6 in theimage obtained after the synchronization error is compensated for to theresult “0.”

[0131] As described above, the image processing apparatus 4 reads apixel value in each line, calculates the logical product of a pixelvalue in a line and that in the line one line before, and sets a pixelvalue in a new image to the calculation result to convert the imageshown in FIG. 13 to the image shown in FIG. 10(C).

[0132] In the above description, the logical product of a pixel value ina line and that in the line one line before is calculated and a pixelvalue in a new image is set to the calculation result. It is alsopossible that the logical product of a pixel value in a line and that inthe line one line after is calculated and a pixel value in a new imageis set to the calculation result.

[0133] A procedure for detecting the position of the bright point by theuse of the image data converted to a spatial pattern, which is obtainedas described above, will be described next.

[0134]FIG. 17(A) shows a case in which the image data of the blinkingpatterns of three bright points Li1, Li2, and Li3 disposed as shown inFIG. 18 are converted to a spatial patterns. To obtain the positions ofthe bright points Li1, Li2, and Li3, the image processing apparatus 4adds pixel values “1” of the bright points disposed on scanning lines inthe direction (in the y-axis direction in this case) in which capturingis performed in the flow pickup method to obtain peaks, as shown in FIG.17(A), and regards the coordinates of the peaks in the x axis as the xcoordinates of the bright points in the image. In this case, the xcoordinates of the bright points Li1, Li2, and Li3 on the image displaysection are X1, X2, and X3, respectively.

[0135] The y coordinates of the bright points where they start emittinglight are regarded as the y coordinates of the bright points on theimage display section. In this case, since the flow pickup direction isnegative, bright points 1, 2, and 3 are the positions where the brightpoints Li1, Li2, and Li3 start emitting. Therefore, the y coordinates ofthe bright points 1, 2, and 3, Y1, Y2, and Y3, are regarded as the ycoordinates of the bright points Li1, Li2, and Li3, respectively.

[0136] In this way, the image processing apparatus 4 obtains the x and ycoordinates, (X1, Y1), (X2, Y2), and (X3, Y3), of the bright points Li1,Li2, and Li3. The positions where the bright points Li1, Li2, and Li3actually exist are detected correspondingly to these coordinates.

[0137] A procedure for detecting the state of a bright point in theimage processing apparatus 4 will be described next by referring to FIG.19.

[0138]FIG. 19(A) shows the spatial pattern of the bright point Li1 shownin FIG. 17. To detect the state of the bright point Li1, the imageprocessing apparatus 4 selects bright points disposed within apredetermined fluctuating range (X−ΔX≦x≦X+ΔX) of the x coordinate X1,adds in the x-axis direction, and obtains peaks as shown in FIG. 19(B).The image processing apparatus 4 then binarizes the obtained peaks bythe use of a predetermined threshold to generate bit-pattern informationshown in FIG. 19(C). With the use of the obtained bit pattern(10101010), the state of the bright point Li1 is detected. In this case,the bright point Li1 blinks with a blinking pattern from which eight-bitinformation is extracted.

[0139] Bright points disposed within a predetermined range in the xcoordinate are selected to obtain a more precise bit pattern. The bitpattern is prevented from being changed due to, for example, an adjacentimage having another spatial pattern.

[0140] The bit pattern obtained in this way is sent to the personalcomputer 5, and then, the same processing as that in the firstembodiment is executed.

[0141] As described above, since the flow pickup method is used in thepresent embodiment, the position and the blinking pattern of a brightpoint can be simultaneously detected in one field.

[0142] Since the position and the blinking pattern of a bright point canbe simultaneously detected, the processing time of the personal computer5 is reduced. The time required for displaying position marks on animage is further made shorter than that in the first embodiment, and aneasier-to-understand presentation system is provided for the audience.

[0143] All stages of a lens section (not shown) of the video camera 3used in the present embodiment may be provided with optical filters. Inthis case, incident light other than that emitted from a bright pointcan be controlled.

[0144] Providing media for providing the user with a personal-computerprogram which executes the above-described processing include recordingmedia, such as magnetic disks, CD-ROMs, and solid memories, andcommunication media, such as networks and satellites.

What is claimed is:
 1. An image processing apparatus comprising:position determination means for determining from image informationindicating a captured second image which includes a bright pointdisposed on a first image the position of the bright point; andblinking-pattern detection means for binarizing the image information todetect the blinking pattern of the bright point disposed on the firstimage.
 2. An image processing apparatus according to claim 1, whereinsaid position determination means compensates the position of the brightpoint on the second image to determine the position of the bright pointon the first image.
 3. An image processing apparatus according to claim1, wherein the second image is taken by a flow pickup method, and saidblinking-pattern detection means converts the image information totwo-dimensional data and binaries the data to detect the blinkingpattern of the bright point disposed on the first image.
 4. An imageprocessing method comprising: a position determination step ofdetermining from image information indicating a captured second imagewhich includes a bright point disposed on a first image the position ofthe bright point; and a blinking-pattern detection step of binarizingthe image information to detect the blinking pattern of the bright pointdisposed on the first image.
 5. A providing medium for providing acomputer-readable program which makes an image processing apparatusexecute processing, said processing comprising: a position determinationstep of determining from image information indicating a captured secondimage which includes a bright point disposed on a first image theposition of the bright point; and a blinking-pattern detection step ofbinarizing the image information to detect the blinking pattern of thebright point disposed on the first image.
 6. An image processingapparatus for processing an image of an object having four points ofwhich the mutual relative positions are known, comprising: firstcalculation means for calculating the gradient of the object in athree-dimensional space from the positions of the four points on theimage; and second calculation means for calculating the position of theobject in the three-dimensional space from the gradient of the object inthe three-dimensional space calculated by said first calculation meansand the distances between the four points.
 7. An image processing methodfor an image processing apparatus that processes an image of an objecthaving four points of which the mutual relative positions are known,comprising: a first calculation step of calculating the gradient of theobject in a three-dimensional space from the positions of the fourpoints on the image; and a second calculation step of calculating theposition of the object in the three-dimensional space from the gradientof the object in the three-dimensional space calculated in said firstcalculation step and the distances between the four points.
 8. Aproviding medium for providing a computer-readable program which makesan image processing apparatus that processes an image of an objecthaving four points of which the mutual relative positions are knownexecute processing, said processing comprising: a first calculation stepof calculating the gradient of the object in a three-dimensional spacefrom the positions of the four points on the image; and a secondcalculation step of calculating the position of the object in thethree-dimensional space from the gradient of the object in thethree-dimensional space calculated in said first calculation step andthe distances between the four points.
 9. A presentation systemcomprising: image display means for displaying a first image; pointingmeans for pointing a predetermined position on the first image by abright point; pickup means for capturing a second image which includesthe bright point pointed on the first image; image processing means fordetermining the position of the bright point on the first image fromimage information indicating the second image and for binarizing theimage information to detect the blinking pattern of the bright point onthe first image; and combination means for combining the first imagecorrespondingly to the position of the bright point and the blinkingpattern of the bright point detected by said image processing means.